The invention relates to a high voltage electrical winding conductor bar for use in a dynamoelectric machine. In particular, it relates to stator bars used in generators where the bars comprise strands of conductors bundled together, insulated from each other by strand insulation and additionally surrounded by groundwall insulation.
The thickness of stator bar groundwall insulation is a limiting factor in an electrical generator stator bar design and in machine output. If the thickness of the groundwall insulation can be reduced, more space would be available for conductors in the same slot. As a result, the size of the conductors can be increased thereby increasing conductor volume and current capacity for the same size bar. Alternately, the bar size could be decreased with no loss in conductor volume, resulting in reduced machine size with associated weight and material cost savings.
Presently, high voltage stator bars are constructed by bundling a number of conductors of copper or aluminum strands that are insulated from each other by strand insulation. The strands of insulation are commonly arranged to form two tiers that can be separated by a strand separator. Alternatively, the stator bar can be constructed with four-tier and six-tier strands. The strands can be arranged in a spiraling manner, also known as Robeling. Top and bottom edge uneven surfaces are created where spiraling conductor strands cross over from one tier to a next tier along the slot length. The conductor bar ends can be leveled or evened by molding a transposition filler to the ends during pressing of the conductor package.
A groundwall insulation can be provided by multiple wrappings of a mica paper tape surrounding the tier strands, strand insulation and transposition filler. The amount of insulation is dependent on the capability of the insulation to survive corner electrical stress concentration. Sharp corners concentrate electrical stress while conductor corner increased radius reduces stress. The general rectangular geometry of a stator bar results in high corner electrical stress.
It is desirable to reduce corner electrical stress. A reduction in electrical stress can result in a reduction in the amount of groundwall insulation, which can allow for additional space for conductors. Or a reduction in corner stress can increase a voltage rating of a dynamoelectric machine by providing generator stator bars that can operate at higher nominal voltage stress. Typically, corner stress is reduced by machining or shaving of strand corners. However, machining decreases strand copper content. Reduction in copper content reduces conductivity. Hence, the strands are machined or shaved only at or near their corners. Typically the copper cross-section in each strand spiraling is reduced up to 0.080 inch, usually 0.060 to 0.080 inch along the bar and typically only at one corner of each strand. Reduction greater than 0.080 inch can result in hot spots or leaks in hollow liquid cooling stator bars.
Hence, there is a need to effectively reduce voltage stress concentration by increasing radius at conductor bar surface corners without significantly decreasing strand copper or aluminum content.
The invention provides a method for making a dynamoelectric machine conductor bar suitable for use in a dynamoelectric machine. The bar has reduced corner stress that is achieved, surprisingly without decreasing strand copper or aluminum content. The method comprises providing a plurality of bundled together spiraling strand conductors having surrounding insulation to define a substantially rectangular shape with the strand conductors and strand insulation defining a conductor bar end portion having an electrically insulated gap between the strand insulation adjacent the conductor bar end portion; and applying a filler material to fill the gap to electrically shield the conductor bar end portion and to define a greater than 0.080 inch continuous outer radius surface end portion.
In another embodiment, the invention is a method for making a dynamoelectric machine having a stator with a high voltage winding comprising a plurality of conductor bars extending along slots in the winding, comprising: providing a plurality of bundled together. spiraling strand conductors having surrounding insulation to define a substantially rectangular shape, with the strand conductors and strand insulation defining a conductor bar end portion having an electrically insulated gap between the strand insulation adjacent the bar end portion; and applying a filler material to fill the gap to electrically shield the conductor bar end portion and to define a greater than 0.080 inch continuous outer radius surface end portion.
The invention also relates to a high voltage electrical winding conductor bar suitable for use in a dynamoelectric machine. The dynamoelectric machine conductor bar comprises a plurality of bundled together spiraling strand conductors having surrounding insulation to define a substantially rectangular shape with the strand conductors and strand insulation defining an opposing conductor bar end portion; an electrically non-insulated gap between the strand insulation adjacent the conductors at the bar end portion; and an applied filler material filling the gap to electrically shield the conductor bar end portion an applied filler material filling the gap to electrically shield the conductor bar end portion, wherein the filler material defines a greater than 0.080 to about 1.5 inch continuous outer radius surface end portion.
In another embodiment, the invention is dynamoelectric machine having a stator with a high voltage winding comprising a plurality of conductor bars extending along slots in the winding, the conductor bars comprising: a plurality of bundled together spiraling strand conductors having surrounding insulation to define a substantially rectangular shape, with the strand conductors and strand insulation defining an opposing conductor bar end portion; an electrically non-insulated gap between the strand insulation adjacent the conductors at the bar end portion; and an applied filler material filling the gap to electrically shield the conductor bar end portion, wherein the filler material defines a greater than 0.080 to about 1.5 inch continuous outer radius surface end portion.